1. Field of the Invention
The invention relates to a novel duplex basket strainer arrangement. More specifically, the invention relates to such a duplex strainer arrangement wherein the shape and structure of the center plug is advantageously different from prior art center plugs.
2. Discussion of the Prior Art
It is known in the art to use strainers in industrial processes which require the straining of fluids. Such straining is required, for example, in such diverse industries as steel mills where cutting oil is recycled via a straining step, and apple juice manufacturing plants where it is necessary to strain out seeds and fibrous remains from the juice to leave a clear juice. The straining elements in the strainers become clogged in time with the particles they are straining out of the fluids, and if only a single strainer were used, it would be necessary to shut down machinery while the strainers were being cleaned or replaced.
To avoid such costly shut downs, the prior art has developed duplex strainers which include two basket strainers. Only one of the baskets is in circuit at any time, and when the basket in circuit gets clogged, the clogged basket is switched out of the circuit, and the second basket is switched in. The operations will now continue with the second basket in circuit, so that the clogged basket can be removed and cleansed or replaced without interrupting operations.
The prior art duplex strainers consist of a casing having receptacles at each end for receiving a separate strainer basket in each receptacle. Separating the strainer receptacles is a center plug receptacle. The center plug is rotatable in the receptacle and is adapted to direct the flow of the fluid to one basket or the other.
As will be appreciated, the plug must include an inflow stage and an outflow stage, and the stages must be in fluid separation from each other. In arrangements presently available, the fluid seal between stages is provided by the shape of the center plug and the co-operating shape of the inner wall of its receptacle. Specifically, the plug is tapered so that its diameter decreases in the downward direction thereof, and the inner wall of the receptacle is correspondingly shaped. Between the inflow and outflow stages of the plug, the outer wall of the plug is in physical, fluid tight engagement with the inner wall of the plug's receptacle to provide the fluid seal between the stages.
To provide the fluid seal, it is necessary that the outer wall of the plug and the inner wall of the receptacle be very precisely machined to within very close tolerances. In addition, the top of the plug receptacle must provide a downward force on the plug, such as by a spring or other means, to ensure that the plug is in tight engagement with the wall of the receptacle at the sealing portions thereof. Thus, when rotating the plug from one position to another, it is necessary to first release the force on the plug.
In addition, because of the close tolerances involved, the strainers can be used only through a limited temperature range, and only within portions of the temperature scale. If an expanded range is required, it is very often necessary to provide a plug of a different material with a smaller coefficient of heat expansion. Also, as the specific place in the temperature scale may effect the performance of the material of which the plug is made, different plugs, of different materials, may be necessary when the strainer is to be used under different temperature conditions.
Thus, the requirement for very close tolerances provides disadvantages which can substantially increase the costs of the strainers.
Further, in presently available devices, the plugs are solid with only circular, curvilinear paths drilled therethrough to direct fluid from the inlet to the top of a basket, and from the bottom of the basket to the outlet. Although such flow paths are provided, there are no means for directing the flow of the fluid through the paths so that there is a substantial amount of turbulence in the flow so that larger sized strainers are required to handle the volume of the system than would be required with a smooth flow through.